I have extensively researched this a while ago. Here is a big comparison table: Comparison of Cloud, Sync & Email services
I tried to find something that offers both features (e.g. editing Office and text files in the browser, 3rd-party integrations, “online-only” files shown in file explorer), openness (Linux app, F-Droid app, WebDAV), and privacy (end-to-end encryption, private payment methods like Monero). But no such provider exists and there’s compromises everywhere.
I think the ones that you should “short-list” for your research are:
- Dropbox
- Filen
- kDrive
- Mega
- Nextcloud
- Proton
- Seafile
- Tresorit
In the end I went with kDrive myself, also because they’re quite well priced, but I really don’t like the lack of end-to-end encryption. I used MEGA before and they were good but I was missing some features.